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Over the last couple of years we have worked on sealing the house better (new siding with house wrap, new windows / doors, caulk, insulation etc), replaced the 2 HVAC systems with a single variable capacity zoned system, sealed the crawl space and replaced the garage doors with insulated doors. Now on to the plumbing.....

Our split level home was built in two phases, the two story (living quarters above garage) and then the main floor (over crawlspace). There is a mixture of CPVC, PVC and polybutylene. The PVC is holding up well, the poly has a couple of seeping joints and the CPVC is getting brittle. On the main level the genius builder put the water lines in the attic. We currently have two small tankless water heaters located within the living space and vented through the ceiling / attic / roof. Each water heater is only good for running one appliance at a time, they both have standing pilot lights and have no efficiency rating.

I am starting the project with a new water heater, a Rinnai RUR199iP. It is Energy Star qualified with an energy factor of .96. It should save us on propane, not enough to offset the cost but that is not the only reason we went with a new heater. The current heaters require a minimum flow of .5 gpm to activate which makes it hard to get hot water out of a faucet at a low rate. The new heater will activate at .25 gpm. Also, the new heater will direct vent, it vents right out the back wall vs having a vertical vent through the ceiling / roof. This will further our ability to seal up the house.

I am using PEX throughout the house, replacing all the old various pipes. I can't decide whether to have a manifold with all home runs or to run a loop through the house. The water heater has a feature that can be enabled that circulates hot water so you have near on demand hot water. I would imagine this would reduce its energy efficiency though. I need to read up on this.

Anyway, here is the new water heater installed.
 

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I can't decide whether to have a manifold with all home runs or to run a loop through the house. The water heater has a feature that can be enabled that circulates hot water so you have near on demand hot water. I would imagine this would reduce its energy efficiency though. I need to read up on this.
One of the main advantages of tankless units is that you don't have to heat water until you need it. Continuously circulating hot water through your pipes will definiely affect energy use, and possibly the shorten water heater's lifespan as well. A small hot water storage tank in the right location(s) may balance efficiency and performance. Take a look at this article (PDF file).

http://www.chandlerdesignbuild.com/files/fhbDecJan08.pdf

I'm not a plumber, but I've been looking into this issue for quite a while due to the length of our hot water plumbing runs.
 

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i ran a pex hot and cold water oversize mains in my case in a attic area with valves at each appliance drop......oversized the pex due to if you use the brass fittings they restrict flow at each joint to one pipe size smaller

also ran a my hot main as a circulating hot water loop....using a main single tank water heater (propane) i figure it costs me about 5-7 $ a month in propane if i turn on the water circulating loop pump (on a timer) i loop out about 80'
 

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One of the main advantages of tankless units is that you don't have to heat water until you need it. Continuously circulating hot water through your pipes will definiely affect energy use, and possibly the shorten water heater's lifespan as well. A small hot water storage tank in the right location(s) may balance efficiency and performance. Take a look at this article (PDF file).

http://www.chandlerdesignbuild.com/files/fhbDecJan08.pdf

I'm not a plumber, but I've been looking into this issue for quite a while due to the length of our hot water plumbing runs.
Maybe since we have owned tankless heaters for the last 20 years we are accustomed to how they work but we dont have issues with the cold water between showers. Also , we know the limitations of our tankless heaters being small so we dont over tax them and drop the pressure.

That article is 12 years old, I wonder if that installer is doing things differently today with the advancements made in the tankless heater systems. There is no way I would add a tank to a tankless system, I would just install a tank and stay away from tankless before doing that.

Our new heater will deliver near 12 gpm, more than enough for multiple appliances. I am also plumbing it in such a fashion that should we desire a second tankless to the farthest run, a small bathroom, we could just install a small tankless in the crawl space.
 

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Discussion Starter #5
i ran a pex hot and cold water oversize mains in my case in a attic area with valves at each appliance drop......oversized the pex due to if you use the brass fittings they restrict flow at each joint to one pipe size smaller

also ran a my hot main as a circulating hot water loop....using a main single tank water heater (propane) i figure it costs me about 5-7 $ a month in propane if i turn on the water circulating loop pump (on a timer) i loop out about 80'
I'll have to look closer at that. I was doing the mains in 3/4" but may have to go to 1". I just cut into 100 foot rolls of 3/4, yuck
 

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I had all the copper plumbing in my house replaced with PEX. I wanted the manifold set up with the pretty red and blue lines. The plumber talked me out of it. He said he would be glad to do it and take my money, but in his opinion it was a waste of $$. So one big loop is what I have.
I don't circulate the hot water, but it does get to each faucet rather quickly.
 

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I really like the manifold setups. They work great and the even the water pressure in the entire house. As a retrofit it might not be the easiest thing to do but I really like how it works in my home.

This is a shot of the plumbing instal I did for my in-laws new house.
 

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I see no reason no to manifold. It reduces the volume of cold water between the heater and the faucet of choice. Meaning it gets there faster.
 

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I have all of my water going through "manifolds", and I put that in quotes because I don't have true manifolds in place. I split my hot water off in to 3 branches for different zones of the house, that way I can kill just a section for repairs/upgrades. The cold splits from my pressure tank in to 2 branches; raw water and filtered. Raw water goes to my hose bibs, filtered water heads to the softener and filter, that way I'm not wasting salt on outdoor uses. Coming out of the filter, I go to 4 branches, 3 mirror the hot water branches and 1 supplies the hot water heater.
 

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Phone is fighting me trying to upload a second photo.
I hope all that stuff in the pic is for some type of multi-zone heating system!!?? :dunno:

if it is for water,, I have no idea what the stuff could be for,,, :flag_of_truce:
 

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I hope all that stuff in the pic is for some type of multi-zone heating system!!?? :dunno:

if it is for water,, I have no idea what the stuff could be for,,, :flag_of_truce:
That is a wall hung propane condensing furnace, 2 zone hot water baseboard heat, an indirect hot water tank, all the near boiler valves and parts to make it work, as well as half of the manifolded hot water for the house.

The furnace is rated at 96% efficiency and does both central heat and domestic hot water. You can stand right next to is and you won't hear it running even at full fire. The hot water is virtually endless. Everything is next to zero maintenance and all the tanks and heat exchangers are made of stainless steel.

I did the installation and it cost me in parts the same amount of money a contractor would have charged for a standard system of half the quality and lower efficiency.
 

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I also went with a Manabloc water manifold.

About 3 years ago now we did what started as a bathroom remodel. We have one full bath in our house and it needed to be redone. That turned into removing 95% of the copper in the house and replacing it with PEX. We went from a traditional water heater to a 199,000 BTU tankless. So the project was somewhat in line with what you are doing. One thing I love about the Manaboc is if you need to shut the water off at a point of use, no need to crawl under the cabinets and mess with seized up valves. I just go down to the Manaboc and turn off that point. If you need to work on something, no need to shut off the water to the entire house. If you are new to tankless there are a few things you should be aware of.

The obvious cost savings is not having to heat water in a large tank when you are not using it. Where the bigger savings probably comes from is where you need to have a bit of a change in mentality on how you use water in your house. With a traditional system you might heat water to 150F. You do this because with a family of 4 needing to take showers, you can get by with a 40 gallon tank by having the hot a lot hotter than what you want to use and mix in cold to bring it. So you are spending money heating up the water hotter than you want, then cooling it back down at the point of use to get to a temp that you want.

So the first lesson to learn is to set the temp to what the hottest temp is that you want to use. Since you don't have a tank that will run out of hot water, you don't have to worry about running out. That brings me to the next point. Many people are used to setting the mixing valves at a certain point with a tank based system. The they go tankless and set the mixing valves the same and wonder why the shower is cold. They then find that they have to turn it fully to hot to get a hot shower. Then they complain. Well yeah it is more efficient this way. However there is a problem. If you have 1/2" supply lines, you may not have enough flow to run just full hot and get the pressure you had when you were running a mix of hot and cold water. Because of this I ran 1" hot water pipe to my shower. No need for that big of a cold line because I don't use much cold. It really was only an issue with the shower. I should add that the shower has a traditional shower head, cloud head in the ceiling and body sprayers so it isn't low flow. Time for the next consideration. I found that the mixing valve I chose is designed to always mix in some cold water. Because of this I am running my tankless system at 122F. It is hotter than I want for a shower but it always will mix in some cold and that lets me get about as hot as I want it.

Overall, I don't have any complaints. It took some education for the family on how to use hot water vs with the old system. We never run out of hot water when the entire family has to take showers. I would not hesitate to do a manifold system again.

This is the Manabloc

Viega ManaBloc distribution manifold | viega.us
 

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We've been using tankless water heaters for 20 years, we knew what to expect...we thought.

Our old tankless water heaters were min 28k btu and max 117k btu with an activation flow rate of .5 gpm. We were use to it and new how to control it but when friends and family would stay over they would complain it was either hot or cold, no in between.

The new tankless heater is min 15k btu and max 199 btu with an activation flow rate of .25 gpm. We now get a better mix of hot and cold making it easier to dial in one's desired temp. We also get hot water out of fixtures at a lower gpm which will save some water I assume.

So far we are very happy with Rinnai RUR199iP
 

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We've been using tankless water heaters for 20 years, we knew what to expect...we thought.

Our old tankless water heaters were min 28k btu and max 117k btu with an activation flow rate of .5 gpm. We were use to it and new how to control it but when friends and family would stay over they would complain it was either hot or cold, no in between.

The new tankless heater is min 15k btu and max 199 btu with an activation flow rate of .25 gpm. We now get a better mix of hot and cold making it easier to dial in one's desired temp. We also get hot water out of fixtures at a lower gpm which will save some water I assume.

So far we are very happy with Rinnai RUR199iP
Ahh, OK I thought you were new to tankless. It is less common at least up here in the great north. I think part of that is because you have to have a unit capable of a pretty big delta in order to heat the water to the desired temp. Some places in the southern states have cold water in the 80F range so it doesn't have to do much work. For us, our cold is in the 50s. We have a 160' deep private well so the temps are pretty constant.

One thing I would watch as I saw some comments on PEX sizing. As I mentioned we went with a really large pipe for hot to the shower. Really our highest volume point of use. More so if you open all the valves. Anyhow with the exception of that we went with 1/2" for cold everywhere and for hot it was either 3/8" or 1/2". To go back and do it over again, I don't know if I would mess with the 3/8" again. Here was the thinking behind it. The only place it was used was bathroom sinks. They are longer runs and as you know water sitting in a hot pipe will just cool off unless you have active heat on the pipe or a re-circulation circuit. I skipped both those options and just live with the hot being cold for a bit. I went with 3/8 thinking that those faucets are all low flow so the more water sitting in hot pipe that is going to get cold anyhow, the bigger the pipe, the more volume that you need to flush out to get hot water. Since the flow rate is restricted at the faucet anyhow, it doesn't make much sense to go with 1" pipe to avoid restrictive elbows or couplers to go through a flow restricted faucet anyhow. In the end of having to buy special fittings and change the crimp tool back and forth, it would probably been easier to just use 1/2" everywhere with the exception of the shower. That was totally worth the 1". I don't know how much more water volume is sitting in 10' of 3/8 PEX vs 1/2 PEX. I am sure that there is a calculation chart somewhere to tell me but to do it again, I would just use 1/2 everywhere. The great thing about PEX is that it is flexible so you really don't need a lot of connections. In fact you don't want them. So I wouldn't worry too much about restriction from them because in the case of a faucet that is your bottle neck. Some might say my shower head is the restriction on my shower. It is to a point but not when I turn on the body sprayers, cloud head and shower head.

Also to touch on the getting guests used to a tankless. The mixing valve that we went with is the style where you have one lever for flow rate and one you use to dial in the temp. The temp is actually calibrated to temp in degrees F. So all they do is set it to 100F or I like a hotter shower so I start at 110F. Then adjust the flow valve. The mixer takes care of the rest in terms of mixing hot and cold. Being incoming water to the mixing valve is 122 (I think that is where I have it set) it is pretty much full hot. When I first was calibrating it I found in the manual that it was set to always let in something like 30% cold water all the time. I had a hard time getting the water hot enough. Then I read the manual and found there was a safety override for homes that us a tankless type heater where the incoming water wasn't dangerously hot and you could reduce that min cold water inlet to something like 5%. I forget the numbers exactly but something like that. Then there there are diverter valves that are used to turn on where you want the water to come out.
 

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When we built our new house on the farm five years ago, we went with a Rheem tankless. We went with the best model that uses PVC for intake and exhaust. I was concerned about my young grandkids touching the concentric on the lesser priced model. It took some getting use to not having instant hot water. But for all the propane we saved, we don't mind waiting. I'd recommend running the hot kitchen faucet first before starting your dishwasher, otherwise your starting wash cycle will be in cool water. Same for you washing machine. We have a drilled artesian well and the water is super cold. The Rheem factory default setting was 120 degrees. Someone posted a video on YouTube on how to change the default setting, I changed ours to 130 degrees. Serves our purposes well.
 

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We had the whole house re-plumbed with pex because the copper kept springing pin hole leaks. I love the manifold system. Want to work on just one faucet? Just turn off the water to that one line instead of heading out into the yard with the big tool and pulling up the water meter lid. That was over 25 years ago.
 

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A few notes.

The rating on tankless heaters is the gpm that can be raised 40f. Except Bosch who publishes gpm for 60f. For me that means I get 1/2 the rating. My rheem 10.9 gpm (200k btu) delivers about 5.5 gpm in winter at bath temps.

I have 1.8 gpm showers and with a manifold feeding 1/2” pex I have no pressure or heat issues even with 2 showers going off separate branches.

I have never heard of using a mixing valve with a tankless setup. I checked with 5 others who had professional installation unlike me and none of them have one. To me it seems they are only a negative. A .5gpm starting flow would need .6 gpm at the faucet to turn on. Also with any type of flow controller it’s best to follow an 80-20 rule. They struggle to control below 20% of their rating or above 80%. This applies to gasses or liquids.
 

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I have never heard of using a mixing valve with a tankless setup. I checked with 5 others who had professional installation unlike me and none of them have one. To me it seems they are only a negative. A .5gpm starting flow would need .6 gpm at the faucet to turn on. Also with any type of flow controller it’s best to follow an 80-20 rule. They struggle to control below 20% of their rating or above 80%. This applies to gasses or liquids.
By mixing valve are you talking about in a shower? If so, if you don't have one do you just use the old school separate valve for hot and cold? We have had no issues with ours once I followed the directions in the manual for it on removing the "safety" for use in an environment like a tankless water heater where the supply hot water isn't as hot as what one would find in a traditional tank system. Not sure what our flow is with the shower but pretty high.

That is true about the 80-20 rule. That is why you want the system sized right. Overkill isn't always a good thing. Like with the garage build the boiler has to be sized right for the same reason. There is a sweet spot for them
 

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By mixing valve are you talking about in a shower? If so, if you don't have one do you just use the old school separate valve for hot and cold? We have had no issues with ours once I followed the directions in the manual for it on removing the "safety" for use in an environment like a tankless water heater where the supply hot water isn't as hot as what one would find in a traditional tank system. Not sure what our flow is with the shower but pretty high.

That is true about the 80-20 rule. That is why you want the system sized right. Overkill isn't always a good thing. Like with the garage build the boiler has to be sized right for the same reason. There is a sweet spot for them
Your posts above talk about mixing valves. I thought you were discussing having one on a tankless supply like you would on a tank or boiler.
 
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